1. Field of the Invention
The present invention relates to a method and apparatus for hot forging powder metal preforms, and more particularly to a fully automated, production method and apparatus for carrying out the method.
2. Description of the Prior Art
The art of hot forging finished articles from powder metal preforms is a relatively new one. Heretofore, this art has involved the provision of a heating furnace and a forging means. The preforms were first heated in the furnace and then carried, in heated condition, to the forging means. This procedure involved a number of workers and was time consuming.
When it was necessary to preform the heating and hot forging steps in a protective atmosphere, such as a non-oxidizing atmosphere, it was the usual practice to insert the preform in a die set and place the entire preform-die set assembly in the furnace. Thereafter, this entire assembly was transferred to the press and the hot forging operation was performed. Under these circumstances, prior art workers relied upon the protective atmosphere, which had penetrated the die set, to protect the preform during the forging operation. Again, this operation was slow and required the use of many tool sets.
Where heating was performed by high frequency electrical energy, the high frequency heating apparatus was generally located in the vicinity of the dies so that the workpiece was heated in the impact forging position. Such a method was taught in U.S. Pat. No. 3,331,686. Under these circumstances it was necessary to heat and forge a workpiece before the heating of the next workpiece could begin.
As a consequence, the practice of hot forging finished articles from powder metal preforms has not lent itself to a high-rate, production process.
Prior art workers have devised systems whereby ordinary forging processes have been automated. Such a system, for example, is taught in British Pat. No. 884,709. However, ordinary forging of preformed blanks is fundamentally different from the hot forging of powder metal preforms into finished products. In the usual forging practice, as exemplified by the above mentioned British patent, the operation may start with preformed blanks. The blanks are characterized by the fact that they are fully dense, wrought or fusion parts. The blanks contain an excess of metal which is lost as flash or the like during the forging operation with the result that the trimmed forged piece weighs less than the initial blank. In ordinary forging operations, the pieces are subject only to surface oxidation which can be readily removed. Finally, the ordinary forging process does not produce a "finished part" within the meaning of that phrase as used herein and in the claims (i.e. a part involving no scale removal and having finished surfaces equivalent to precision machined surfaces). In the ordinary forging process the blanks are subjected to one or more forging steps (the above noted British patent teaches two) followed by machining or the like.
The hot forging of powder metal preforms, on the other hand, is wholly different. First of all, the powder metal preforms are porous structures, as opposed to the dense metal preforms for ordinary forging. While the hot forging of powder metal preforms may and generally does involve a change in shape, it is primarily a densification or consolidation step. There is no flash and no loss of material, the forged part weighing the same as the powder metal preform. This is extremely significant because it means that oxidation cannot be tolerated.
Unlike ordinary forging preforms, powder metal preforms are subject to both internal and external oxidation. Internal oxidation (the metal being porous) must be avoided because such oxidation would be trapped within the metal preform, seriously affecting its properties. External oxidation is similarly to be avoided. Since all of the metal of the powder metal preform is used to form the final product, none can be lost to external oxidation.
Finally, unlike ordinary forging processes, the hot forging of powder metal preforms produces in one forging blow a finished product having surfaces equivalent to precision machined surfaces.
The present invention is directed to a method and apparatus whereby the hot forging of finished articles from powder metal preforms may be accomplished inexpensively, at a high production rate and fully automatically. The hot forging method of the present invention may be practiced by a single operator. The process and apparatus results in a considerable economic savings in materials and the number of steps required to produce the final product. The process may include a sintering step so as to comprise a fully automated, production process from the compacting press to the final product. The final product, itself, demonstrates properties and characteristics equivalent to or superior to products produced by ordinary forging processes.